Liquid-cooled electric machine, particularly turbo-generator

ABSTRACT

A liquid-cooled electric machine, such as a turbo-generator, has a stator with a multi-phase double-layer lap winding composed of winding portions, main current feed-throughs, and circuit connectors. The circuit connectors form electric circuit-group connections between the winding portions and also connect the winding portions with the feed-throughs. The stator comprises a liquid-coolant system which has two hydraulically parallel connected branch groups of coolant ducts. A first one of these duct groups extends through the multi-phase winding. The second branch group of ducts extends through the feed-throughs and the connectors. Insulating hose members form part of the second branch group and fluidically bridge each two of those connectors that have instantaneous potentials, i.e. have different electrical potentials or assertain to different phases. A plurality of hydraulically parallel cooling branches of the second group is formed by the hose members and those of said connectors that are electrically located between each two of the feed-throughs. The connectors form a ring conductor arrangement, and each of said cooling branches between two respective ones of said feed-throughs has a portion which extends through the geodetically topmost region of the arrangement. At least one insulating coolant discharge line is connected to this topmost portion, the coolant being conducted in the cooling branch between the two feed-throughs and the associated discharge line in double-stream fashion. A coolant collector tank with an internal gas cushion space is mounted geodetically above the topmost ring conductor portion. The coolant discharge line forms a riser communicating from below with said tank so as to pass not only coolant but, due to buoyancy, also entrained undissolved gas into the tank.

United States Patent [1 1 Beermann et al.

[ LIQUID-COOLED ELECTRIC MACHINE,

[73 Assignee: Siemens Aktiengesellschatt, Berlin and Munich, Germany[22] Filed: July 20, 1971 [21] Appl. No.: 164,367

[30] Foreign Application Priority Data July 30, 1970 Gennany; P 20 37794.0

[52] US. Cl. 310/54, 310/198, 310/206 [51] Int. Cl. H02k 9/00 [58] Fieldof Search 310/54, 53, 58, 59, 310/62, 63, 64, 65, 184,207,206, 198, 180

[56] References Cited UNITED STATES PATENTS 2,970,232 l/l961 Kilboume310/54 3,594,595 7/1971 Williams 310/207 2,934,655 4/1960 Heller 310/582,975,308 3/1961 Kilbourne 310/54 3,089,969 5/1963 Wiedeman 310/582,675,493 4/1954 Grobel 310/53 3,318,253 5/1967 Campolong 310/54 PrimaryExaminer-R. Skudy Att0rneyCurt M. Avery, Herbert L. Lerner et al.

[5 7] ABSTRACT A liquid-cooled electric machine, such as aturbogenerator, has a stator with a multi-phase double-layer lap windingcomposed of winding portions, main cur- [451 Aug. 14, 1973 rentfeed-throughs, and circuit connectors. The circuit connectors formelectric circuit-group connections between the winding portions and alsoconnect the winding portions with the feed-throughs. The statorcomprises a liquid-coolant system which has two hydraulically parallelconnected branch groups of coolant ducts. A first one of these ductgroups extends through the multi-phase winding. The second branch groupof ducts extends through the feed-throughs and the connectors.Insulating hose members form part of the second branch group andfluidically bridge each two of those connectors that have instantaneouspotentials, i.e. have different electrical potentials or assertain todifferent phases. A plurality of hydraulically parallel cooling branchesof the second group is formed by the hose members and those of saidconnectors that are electrically located between each two of thefeedthroughs. The connectors form a ring conductor arrangement, and eachof said cooling branches between two respective ones of saidfeed-throughs has a portion which extends through the geodeticallytopmost region of the arrangement. At least one insulating coolantdischarge line is connected to this topmost portion, the coolant beingconducted in the cooling branch between the two feed-throughs and theassociated discharge line in double-stream fashion. A coolant collectortank with an internal gas cushion space is mounted geodetically abovethe topmost ring conductor portion. The coolant discharge line forms ariser communicating from below with said tank so as to pass not onlycoolant but, due to buoyancy, also entrained undissolved gas into thetank.

5 Claims, 5 Drawing Figures United States Patent [191 [111 3,753,013Beermann et al. Aug. 14, 1973 Pmmmwm ma 3 753 013 sum 1 UP 4 PAIENTEUAHB1 9 5 3 753 ()1 sum 3 or 4 LIQUID-COOLED ELECTRIC MACHINE, PARTICULARLYTURBO-GENERATOR Our invention relates to liquid-cooled electricmachines, particularly those of high power rating, such asturbo-generators, whose stator winding is of the multiphase double-layerlap type connected to main current feed-throughs, and whose individualwinding portions are connected with each other and with the feedthroughsby means of circuit connectors. The machine stator is provided with aliquid-cooling system which has two hydraulically parallel coolingbranch groups. One of these branch groups is constituted by coolantducts in the stator winding. The second branch group extends throughrespective ducts in the feed-throughs and the circuit connectors.

A liquid-cooled electric machine of this kind is known (German publishedPatent Application No. 1,184,852). It is essential that a liquid-coolingsystem of such a machine provides for direct cooling of not only theconductors of the winding but also of all other machine parts in whichheat due to electric losses can be generated. For this reason,particularly the ringshaped coolant connections, like the windingconductors, are designed as hollow conductors traversed by the flow ofthe cooling liquid. To afford passing the required quantity of coolantthrough the cooling duct cross sections per unit time, the coolant isnot fed to the cooling ducts of the stator winding in series but isconducted within a separate cooling branch group through the ducts ofthe high-current feed-throughs and of the circuit connectors all the wayto the junctions of the connectors at the stator winding.

In the known electric machine, the cooling ducts of the two main-currentfeed-throughs are always connected flow-wise in series, so that thecooling liquid flows upwardly through the respective cooling ducts fromone main-current feed-through via the ring conductor parts of theconnectors all the way to the junctions of the connectors at the statorwinding and thence returns downhill to the other main-currentfeedthrough via other ring conductor or connector parts connected toother peripheral points of the coil ends. Connector junctions which areat different potential or belong to different phases are fluidicallybridged by hose sections of insulating material, so that relativelyshort pieces of insulating tubing result and the length of theconnectors is kept within tolerable limits.

Due to the fact that the cooling liquid flows between the respective twomain-current feed-throughs through the cooling ducts of the connectorsfirst uphill and then downhill to the coolant exit, difficulties areencountered in that gas bubbles rise from the low coolant inlet oroutlet to the topmost part of the cooling duct and can accumulate in theupper regions of the duct. This may impair the cooling effect unlessprovisions are made for reliably venting the cooling water flowingthrough the cooling ducts of the feed-throughs and of the connectors andinsulating tubes. As is well known, protective gas components get intothe stator coolant circulation because the stator housing is filled withprotective gas of higher pressure than the pressure level of the'coolingliquid. Consequently, the protective gas diffuses through the insulatingtubing, usually of Teflon (tetrafluorethylene), into the coolantcirculation of the stator winding and into the circulation of thecircuit connectors and feed-throughs. Protective gas or such gas as H,or N,, for instance, may be contained in the cooling liquid also for thereason that the coolant should besaturated with these protective gasesfor excluding O 2 components which are undesirable in the coolantbecause of the danger of corrosion, and that a simple leak indication bymeasurement of the gas concentration is made possible in this manner. Itis a principal object of our invention, therefore to prevent the dangerof gas-bubble or gas-cushion formation as might impair the coolant flowin the circuit connectors and insulating tubing, in a reliable andsimple manner and while preserving the applicability of a gas filling onthe machine housing and the occurrence of gas components in the coolingliquid.

To this end, and in accordance with our invention, the cooling liquid isconducted within the second cooling branch group in such a manner thatseveral parallel cooling branches of the second cooling group are formedby the circuit connectors situated between each two high-currentfeed-throughs; and the sections of insulating hose, which fluidicallybridge different circuit connectors of instantaneously differentpotential, i.e. that may belong to different phases or have differentvoltages. Furthermore, the respective cooling branches provided betweentwo high-current feed-throughs have at least one ring conductor sectionincluding the geodetically highest region of the ring conductorarrangement of the circuit connectors, to which section at least oneinsulating coolant discharge line is connected in such a manner that thecoolant is conducted in the respective cooling branch between the twohigh-current feed-throughs and the associated discharge line indouble-stream fashion, the coolant discharge line being designed as atwin line which opens into a coolant collecting tank with an internalgas cushion. The tank is arranged geodetically above the topmost ringconductor section. As a result, the discharge line rising from below upto the tank, passes not only the coolant but, due to buoyancy, also anyundissolved gas into the tank.

By virtue of the invention the formation of gas bubbles or gas cushionsat bends or in downhill connecting conductor sections is reliablyprevented. At the same time, due to the double-stream conduction to thehighest-situated discharge point, a more intensive cooling of thefeed-throughs and circuit, connectors or ring conductors isaccomplished. There result relatively short cooling paths within theconnectors so that the flow resistance is relatively small. Furthermore,very short connections are obtained between the coolant discharge pointand the collecting tank disposed in the upper peripheral region of themachine via the insulating discharge lines. An effective venting issecured by connecting the coolant discharge line to the respectivehighest tap point of the ring conductor section. Even if connectors orinsulating hose sections are led downhill for short distances, thecooling is not impaired because the flowing liquid transports any hereevolving gas bubbles to the upper tap point.

Depending on the selected flow velocity, and according to anotherfeature of our invention, the coolant ducts of the circuit connectorsand insulating hose sections situated between the connection of thecoolant discharge line and the respective high-current feedthrough, arepreferably given a slope so as to avoid the formation of gas bubbletraps. For the same reason it is preferable to avoid extreme bends inthe line.

According to a preferred embodiment of the invention, the machine isprovided with a three-phase stator winding in simple Y connection, andsix high-current feed-throughs are associated in pairs with each statorwinding circuit, external circuit connectors establishing the electricalconnection between the high-current feed-through and one end of thewinding circuit, whereas internal circuit connectors (group connectors)electrically connect respective parts of winding circuits turns or coilsin series. The cooling liquid of the second cooling branch group is ledin six parallel streams through the connector cooling ducts. Eachindividual stream flows through the series-connected cooling ductsections of a high-current feed-through, a circuit connector, aninsulating hose section fluidically bridging the phase jump to the groupcircuit connector of another winding circuit, and of part of thehighestsituated section of the ring conductor whence the flow streamreaches the connection of the coolant discharge line.

The invention is also applicable to machines with a multiphase,particularly three-phase, stator winding in multiple Y connection, forinstance, double-Y connection. The coils situated diametrically oppositeon the circumference of such a machine in double-Y connection areconnected in parallel as is well known.

As to the electrical and coolant-wise connection of the circuitconnectors with respect to the feed-throughs and the individual parts ofthe winding, care should be taken that as far as possible no currentloops around the rotor axis are formed which would produce a magneticfield in the direction of the shaft axis, or that the magnetic fields ofsuch current loops are mutually cancelled out, as otherwise a unipolarflux could develop in the region of the rotor bearing of the generatorshaft. This particular problem assumes special significance for largeturbo-generators in the power range of 400 MVA and more, to which ourinvention preferably relates. This significance is due to the fact thatthe unipolar voltages generated between the running surfaces of therotor shaft and the bearing sleeves can cause currents that may damageor ultimately destroy the rotor bearings.

According to a further embodiment of our invention, a particularlyadvantageous arrangement and connection of the circuit connectors andring-conductors, for the prevention of bearing currents caused byunipolar voltages, is provided by electrically connecting and arrangingthe circuit connectors between each two highcurrent feed-throughs of oneof the respective winding circuits or winding phases, in such a mannerthat the current loop sections which are formed by the connectors andwhich produce a magnetic field in the direction of the rotor axis,extend excentrically to the rotor axis and in virtually bifilar fashion.

In the following the invention will be explained in further detail withthe aid of the accompanying schematic drawings which exemplify twoembodiments of the invention in simplified presentation, omitting partsnot essential to the invention.

FIG. 1 shows diagrammatically an electric machine with a stator windingin a simple Y connection, and more specifically the appertaining coolantcirculation system which comprises a first branch group for the statorwinding of the electric machine on the one hand, and the second coolingbranch group for the maincurrent feed-throughs and the circuitconnectors on the other hand, for clarity, the ring conductor parts ofthe circuit connectors being represented not axially one behind theother (as seen in the direction of the axis of the machine), but arearranged concentrically to each other.

FIG. la is a development of the stator winding, the inlet and outletpoints of the coolant being indicated at both end faces of the machine;

FIG. lb is a view of a corrugated tube of insulating material with metalfittings at both ends, serving as an insulating section in the machineaccording to FIGS. 1 and la.

FIG. 2 is a section of FIG. I with the circuit connector arrangement atone end face of the machine, the electric circuit being shown within thecurrent loop sections.

In contrast to FIG. 1, FIG. 3 shows diagrammatically a modified circuitconnector arrangement of the second cooling branch group for a statorwinding with double-Y connection.

The particular electric machine shown in FIG. 1 with a section of thecooling system for its stationary parts is a turbogenerator of highelectrical power rating such as 400 MVA or more. The machine has twofluidically parallel cooling branch groups, namely a first branch groupKI for cooling the stator winding and K2 a second branch group forcooling the main current feedthroughs, generally designated with D, aswell as of the circuit connectors, generally designated by R, whichestablish the circuit-group connection between the individual parts ofthe stator winding generally designated by W, and from the latter to themain current feed-throughs D. As shown in FIG. la, the stator winding Win this embodiment is a three-phase, double layer lap winding. Thecooling liquid is delivered by a pump 1, which may rotate with the rotor(not shown) or a stationary pump. The coolant flows through a linesection I, to a heat exchanger 2 and thence via a line section 1 througha fine filter 3 to the main supply line 1 Part of the cooling liquidpasses through a line branch and a filter bed 4, which usually containsan anion and cation exchanger for removal of 0 CO Cu and otherundesirable ions from the cooling water. From filter bed 4, the coolantreturns through a line section 1 to the pump 1.

The above-mentioned pumping, cooling and processing 1 to 4 furnishtreated and cooled cooling water to the main supply line 1 from whichthe water passes on the one hand, through the cooling branch group KI ofthe stator winding and, on the other hand, through the second coolingbranch group I42. I-Iydraulically the two branch groups are connected inparallel. The warm water, leaving the two cooling branch groups, passesthrough line sections and 1 respectively, to a collecting tank 5 whichis arranged in the upper part of the machine housing and in principlehas approximately the shape of a U. (Connection points 1 1-,). Thecollecting tank 5 has a space 501 for the liquid and a gas space 51;arranged above it, hydrogen being preferably present as the inert gas inthe gas space. The liquid pumped into the leg 50 of the collecting tank5 flows, countercurrentwise to the gas entering into the gas space 5b,through an interconnecting piece 5d to the other tank leg 5e. From leg5e, the water is drawn off, saturated with gas, by the pump I via a lineI This line 1,, therefore, is the main outlet line for the coolingliquid.

The contour line 6 represents the outer contour of the electric machine.The stator winding W is indicated in the left-hand part of FIG. 1 inperspective with but a few turns, in order to show the coolant flowwithin the stator winding. The stator winding W extends from the endface A of the machine (drive side) to the end face B of the machine(exciter side). The circuit connector arrangement R is disposed on sideB of the machine. The cooling liquid is fed by a ring-shaped manifoldarrangement 7, shown symbolically and on a reduced scale, whichcoolant-wise is connected by the line I, via an insulator i to the inletpoints e disposed in the region of the end turns at face A of themachine. This connection comprises line sections 1 insulating hosespreferably of Teflon. The inlet points e serve as the electrical andcoolant connection of the individual stator winding conductors s (upperand lower conductor rods) which are interconnected to form the windingturns s,. After flowing through one winding turn s, the cooling liquidreaches a coolant discharge point a near the periphery and thencepasses, through discharge lines l, containing insulating hose sections,to a ringshaped discharge manifold 8 on the same end face of themachine.

From discharge manifold 8 the cooling liquid passes through a furtherinsulator i, to the line I, and from there to the collecting tank 5,which is at ground potential, as indicated at 9. At the end face B ofthe machine the individual stator winding conductors s of a winding turns, are connected by a connector u (not shown in detail) which serves tochange the flow direction and to also form an electrical connection. Theelectrical and coolant circuits of the stator winding with theirconnection points el, al and u are shown in detail in FIG. 1a.

In the embodiment of FIG. 1 the stator winding W, a three-phasedouble-layer lap winding in simple Y connection, is connected togetherwith the six feedthroughs dll, d12, (121, 4122, (131, d32. Such a feedthrough is schematically indicated at (121. It has two parts 10a and 10bfor conducting the electric current and the cooling liquid, which areenclosed by a hollow, cylindrical insulator (not shown in detail). Part10a extends through the wall of the housing 6 and is con nected with thelatter. Part 1012 is connected with the circuit connector arrangement R;to compensate for different thermal movements between the parts 10a and10b, the latter being connected together via flexible conductor ribbons11 and correspondingly flexible hose sections 12. Flexible, insulatinghose sections for the supply of the coolant from a manifold 13 to therespective feed-throughs are designated by 14. The distribution line 13is supported against its'base by suitable insulators i3 and is connectedcoolant-wise via the in serted insulating section i4, with the mainsupply line 1,, as is the line 1,, of the first cooling branch group Kl.

In principle, the insulatingsection i4, the insulating sections i1, i2and the insulating section i5, further described below, are designed asshown in FIG. 1b. They contain a flexible, corrugated tube 15.,preferably of Teflon, which is tightly connected at both ends 15a. 15!;by flange bodies 16a, 16b to two flanges 17a, 17b of the lines L, Lwhich are to be interconnected by the insulating section 45.

In the embodiment of FIG. 1, the electrical connection between the maincurrent feed'throughs and the stator winding W is such that always twowinding circuit halves or coils, W1]. and W12, W21 and w22, W3! and W32,respectively, are interconnected by a ring conductor section rl, r2 orr3 to form a winding circuit; and these three winding circuits orwinding phases are connected at their two ends by two external circuitconnectors to the corresponding pair of feed-throughs. Specifically, theseries circuit wll r1 w22 (phases U, X) is connected by the connectorsr11, r12 to the main current feed-throughs dill, dl2; the series circuitw2l r2 w22 (phases V, Y) is connected by connectors r21, r22 to the maincurrent feed-throughs d2l, d22; and the series circuit W31 r3 W32(phases W, Z) is connected through connectors r1, r2 to the main currentfeed-throughs d3l, 0'32.

The connections rl, r2, r3 are internal circuit connectors, i.e., theyserve to connect two coils or circuit halves belonging to one windingcircuit in series and are therefore designated as group circuitconnectors. The phase symbols U, V, W; X, Y, Z are shown also at themain current feed-throughs for the sake of clarity. The individualcircuit halves wll, w12 etc. are indicated only symbolically in thecentral part of FIG. 1; their exact mutual relation is shown in thedevelopment according to FIG. la, where the external and internalcircuit connections, the association of the individual phases with theirfeed-throughs d1 1, d12, etc. as well as the phase designations U, V,etc. are entered, the phase designations applying to counter-clockwiserotation from the drive side A.

In addition to the high-current feed-throughs D, the circuit connectorsand ring conductors, respectively, generally designated by R, are alsoprovided with internal coolant ducts extending all the way to theirjunctions 18, relative to the stator winding W and relative to therespective connection rods (see FIG. la).

The flow of the cooling water is shown in FIG. 1 by the arrows k. Forinstance, the water flows from the cooling ducts of the main currentfeed-through dll through the cooling ducts of the connector 111 all theway to thejunctions 18 at the winding wll, from here via an insulatinghose section :1, preferably consisting of PTFE or teflon(polytetrat'luor-ethylene) to the junction 18 of the ring line r3 forwinding w32 and from here via a first partial section r3 of thelast-mentioned ring line to the connection 19 of a coolant dischargeline 20a. The path of the cooling water from the other main currentfeed-through 1112 of the same winding circuit extends similarly throughthe respective cooling ducts of the circuit connector r12 all the way toits junction 18 with the winding W12, thence via the insulating hosesection I2 to the internal connector r3 and via the other partialsection r3 of this connector to the junction 19 of the coolant dischargeline 20a.

It will be seen that the insulating hose sections :1, t2 and analogouslythe other insulating hose sections t3 to M3 bridge coolant-wiserespective circuit connectors of different phases and potentials in sucha manner that very short lengths of the connecting sections and hence ofthe coolant paths are secured. The path of the coolant from the maincurrent feed-through pairs d2! 1122 and d3! d32 to the correspondingconnections 19 of the coolant discharge lines 20b and 20c, respectively,is analogous to the coolant path described above between thefeed-throughs d1 1, dl2 on the one hand, and the connection 19 of thecoolant discharge line 20a on the other hand, i.e. the cooling branchesux, vy, wz, provided between each of two high-current feedthroughs dilldl2 and d2l 1122 and [131 r132, respec tively, each exhibit at least onering conductor section r1, r2 or r3, which includes the geodeticallyhighest region of the ring conductor arrangement of the circuitconnectors R and to which at least one insulating coolant discharge line2%, 20b or 2tlc is connected in such a manner that the coolant in therespective cooling branch between the two high-current feed-throughs andthe associated discharge line 263a, 20b, 29c is conducted indouble-stream fashion. (Streams uxl, ux2; vyl, vy2', wzl, W12,respectively). The respective discharge lines 20a, 2tlb, 20c aredesigned as risers and communicate with the coolant collecting tank 5located above the highest-situated ring conductor section r1, r2, r3,respectively. As mentioned, the tank 5 has a gas space or gas cushion512 so that, aside from the coolant coming from one circuit connectorcooling ducts, the undissolved gas components contained in the coolantcan also enter into the tank 5 due to their buoyancy.

The three discharge lines 2th, b, 20c are connected to a commoncompensator is designed as already explained in connection with FIG. lb.The other end of compensator i5 is connected with the line I, whichopens into the collecting tank 5. If desired, sev' eral compensators IS,one for each discharge line, may be provided. As shown, the coolantducts of the circuit connectors R situated between the respectiveconnection 19 of the discharge lines 20a, 20b and 20c and the respectivehigh-current feed-through D and the insulating hose sections :1 to to,are given a slope which prevents the formation of gas traps. A slightslope for the cooling water, such as that of the circuit connectors rl land r3, before the coolant is again conducted uphill to the connectionpoints W, is not detrimental if extreme bends are avoided, as alongthese relatively short downhill sections the coolant is capable, atsufficient flow velocity, to entrain all gas components.

As can be seen from FIG. 2, the circuit connectors situated between eachtwo high-current feed-throughs dll dl2, d21 d22, d3ll 4132,respectively, associated with one winding circuit or winding phase, areelectrically connected and arranged so that the current loop parts m1,m2, m3 formed by the respective connectors and producing a magnetizationin the direction of the rotor axis I, extend excentrically to the rotoraxis and are virtually bifilar, this being indicated schematically inthe lower part of FIG. 2 by curved arrows giving the direction of thecurrent relative to the shaft.

In the upper part of FIG. 2, which, although greatly simplified,corresponds to FIG. 1, the directions of current flow in the threewinding phases 1, II, III prevailing at a given instant are shown bysolid lines and arrows e! for the feed-throughs, connectors and windingsof the winding phase I. The current flow lines and direction for thewinding phase II are shown by dashed lines; and the conductors andarrows indicative of the current flow direction of the winding phase IIIare shown by dot-dashed lines. A comparison between the upper and lowerparts of FIG. 2 thus permits recognizing the current direction and thecorrelated arrangement of the connectors and ring conductors, the samereference characters being applied in FIGS. l and 2 for correspondingelements respectively.

In FIG. I each of the highest-situated ring conductor sections r1, r2,r3, to which the coolant discharge lines 20 to 201) are connected, issubdivided by connecting points 19 into two circuit connector or ringconductor sections r1 and r1", r2 and r2", r3 and r3", respectively. Theflow of the coolant is in opposite directions in the two line sectionssubdivided by the connecting point 19. Hence, there is a double flowfrom two directions toward the connecting point I9. Within the twocooling branch groups Kl, K2, the supply distribution line 7 and thedischarge manifold 8, as well as the sup' ply distribution line 113 andthe discharge manifold arrangement 20a, Ztlb, 20c, are coolant-wiseconnected with the cooling branch parts at ground potential via theabove-mentioned insulating sections with metal fittings in the form ofcompensators, corrugated tubing and the like ill, 12, i3, i4, i5. Thishas the purpose that, with the cooling branches filled with water, aprecise insulation test of a stator winding phase or a winding circuitcan be performed. This is because the other winding circuits and coolingbranch parts, through which the current for measuring instrument M,serving to indicate leakage current or insulating resistance, is notsupposed to flow, can be brought to the same potential different fromground potential, at the voltage terminal 21 to which the winding to bemeasured by instrument M is connected. For illustration, the plusterminal 2ll of the voltage source 23 is connected in FIG. I to the oneend of the winding wl2 via the measuring instrument, an ammeter orohmmeter, the minus terminal of the voltage source 23 being grounded.The leakage current flowing to ground through the insulation, andtherefore the regular condition of the winding insulation, can now beread at the measuring instrument. However, all of those winding circuitconnectors and cooling branches whose leakage currents would falsify themeasurement, are also connected to plus potential via further plusterminals 22. Hence such leakage current is not conducted through themeasuring instrument M and cannot falsify the measuring result.

The plus terminals are shown connected to the connector-windingjunctions R8 of the windings W31 and w2fl or to the feed-throughs 1121,c122, d3l, (132, as well as to the fitting of the insulating section i5.As will be seen, this insulating section makes it possible to connect toplus potential the fitting of the insulating section i5, which facesaway from the coolant collecting tank 5. Similarly, the supply line 13to the current feedthroughs, which is suspended insulated and isseparated from ground potential by an insulating section i4, isconnected to ground potential. In the left-hand part of FIG. 2, the samepossibility of measurement is indi cated, in order to illustrate thatthe distribution line 7 and the manifold 8 also must be connected toplus potential at the end face A of the machine, the insulating sectionsii, 12 serving the same purpose as the insulating sections i5.

In FIG. 3 the stator winding W is shown double-Y connected electricallywith the feed-throughs D by its circuit connectors. Two diametricallyopposite windings wit and M12, w2l and W22, will and W32, respectively,are connected in parallel to the corresponding pairs of feed-throughsdllll d112, d2l d22, d3l. d32- Each of the cooling branchesux, zw and vybetween two high-current feed-throughs of the circuit connectors areprovided approximately in the middle region of their cooling pathlengths, with highest-situated ring conductor section r31, r32 r21", r32and r11. Each of these ring conductor sections has a connection point I9approachable by two streams and has at least one each coolant dischargeline 24a, 24b, 24c, 2411, 24c. Here, the respective coolant streamsbelonging to one connection point T9 are not in all cases associated totwo feed-throughs for the same winding piece; rather, two coolingbranches uzl, uz2, for instance, are situated between the feed-throughsdll and d32. The one branch uzl extends from the circuit connector r11of the feed-through dll, through the junction 25a and the ring conductor:11, to the connection point 19 of the discharge line 2442 and fromthere via the second section of the ring conductor rll to the insulatinghose section t7, and through this insulating hose section via thecircuit connector r32" and the junction point 25b to the circuitconnector r32 of the feed-through d32. Another cooling branchhydraulically parallel to the above-mentioned cooling branch extendsbetween the branch points 250 and 25b of the circuit connectors r11 andr32 via the circuit connector r11, the insulating tubing 26 to thecircuit connector r32 and to a connection point 19 of the discharge line24d, and from there through the remaining section of the circuitconnector r32 to the connection point 2512. These two circuit connectorcooling branches uzl and uz2 are therefore subdivided by the connectionpoint 19 with discharge lines 24d, 24a into four coolant streams uzll,uzl2, uz2l, uz22. Analogously obtained for the two cooling branches xwland xw2 between the feedthroughs (112 and d3], with the insulating tubes:9 and 210, are four coolant streams xwll, xwl2, xw2l and xw22. Aninsulating hose section t9 is arranged in the stream xwl2, and aninsulating hose section tl in the stream xw 21. The branching points ofthe circuit connectors r12 and r31 are denoted by 26a and 26b,respectively.

As the circuit connectors r21 and r22, associated with the feed-throughsd21 and d22, are brought directly to the connection points 18 of thewinding W21, a cooling branch vy is obtained between these twoconnection points 18. More specifically, the branch vy extends throughthe ring conductor r21 all the way to the connection point 19 of thedischarge line 240 and thence through the other section of the ringconductor r21" and via the insulating hose section 111 to the ringconductor r22" and back to the other connection point 18. This coolingbranch is accordingly subdivided by the connection point 19 of thedischarge line 240 into two streams vyl and vy2. The direction of flowof the coolant is indicated by arrows It.

It will be seen that all ring conductor sections including thehighest-situated region ofthe ring conductor arrangement S, are eachprovided with a connection 19 of the discharge line arrangement 24a to240. In this embodiment provision is made to keep the coolant paths asshort as possible. To this end, parts of circuit connectors or ringconductors belonging to different phases or being at differentpotentials, are connected coolant-wise with each other by the insulatinghose sections :7 to :11. In the embodiment of FIG. 3 there are thusobtained six parallel main treams uzl, xwl, xyl, vy2, xw2, uz2 of thecoolant in the region of the six high-current feed-throughs. This, onthe basis of the electrical parallel connection of the winding parts,results in more mutually parallel coolant streams of the circuitconnectors than in the embodiment of FIG. 1. That is, the embodiment ofFIG. 3 has parallel streams uzll, uz12, uzZl, r4 22, vyl, vyZ, xwll,xwl2, xw2l and 22. The individual discharge lines 24a to 24 open into amanifold 27 which is connected to the line 1 containing the insulatingsection [5. Otherwise, the reference characters in FIG. 3 correspond tothose of FIG. 1 for corresponding elements respectively. The arrangementand mode of operation are analogous to those of the embodiment accordingto FIG. 1.

Upon a study of this disclosure it will be obvious to those skilled inthe art that the invention disclosed herein can be modified in variousways and may be given embodiments other than those illustrated anddescribed herein, without departing from the essential features of ourinvention and within the scope of the claims annexed thereto.

We claim:

I. A liquid-cooled eiectric machine having a threephase stator windingin simple Y connection, such as a turbo-generator, with a stator havinga rnulti-phase double-layer lap winding composed of winding portions,main current feed-throughs, six of said feedthroughs being associated inpairs with each one of said stator winding circuits, and circuitconnectors which form electric circuit group connections between saidwinding portions and which connect said winding portions with saidfeed-throughs, said stator comprising a liquid-coolant system having twohydraulically parallel connected branch groups of coolant ducts of whicha first one extends through said multi-phase winding, the second branchgroup extending through said'feedthroughs and said connectors,insulating hose members forming part of said second branch group andfluidically bridging each two of said connectors that have differentinstantaneous electrical potentials respectively, a plurality ofhydraulically parallel cooling branches of said second group beingformed by said hose members of those of said connectors that areelectrically located between each two of said feedthroughs, saidconnectors forming a ring conductor arrangement, each of said coolingbranches between two respective ones of said feed-throughs having aportion extending through the geodetically topmost region of saidarrangement, at least one insulating coolant discharge line connected tosaid topmost portion, a coolant collector tank with a gas cushion spacemounted geodetically above said topmost ring conductor portion, saidcoolant discharge line forming a riser communicating from below withsaid tank so that said riser conducts into said tank not only coolantbut, due to buoyancy, also entrained undissolved gas, said circuitconnectors comprising external terminal connectors which establish theelectrical connection between said feedthroughs and an end of thewinding circuit, and internal circuit-group connectors whichelectrically series connect respective parts of said windings, saidsecond cooling branch group forming six hydraulically parallel flowpaths through the cooling ducts of the connectors, each individual oneof said six paths extending through the series-connected cooling ductsof a feed-through, a circuit connector, an insulating hose sectionfluidically bridging the phase jump to the group circuit connector ofanother circuit of the winding, and thence through part of said topmostportion of said ring conductor to the cooling discharge line.

2. A liquid-cooled electric machine having a threephase stator windingin double-Y connection, such as a turbo-generator, with a stator havinga multi-phase double-layer lap winding composed of winding portions,main current feed-throughs, six of said feedthroughs being pairwiseassociated with each of the stator winding phases, and circuitconnectors which form electric circuit group connections between saidwinding portions and which connect said winding portions with saidfeed-throughs, said stator comprising a liquidcoolant system having twohydraulically parallel connected branch groups of coolant ducts of whicha first one extends through said multi-phase winding, the second branchgroup extending through said feedthroughs and said connectors,insulating hose members forming part of said second branch group andfluidically bridging each two of said connectors that have differentinstantaneous electrical potentials respectively, a plurality ofhydraulically parallel cooling branches of said second group beingformed by said hose members of those of said connectors that areelectrically located between each two of said feedthroughs, saidconnectors forming a ring conductor arrangement, each of said coolingbranches between two respective ones of said feed-throughs having aportion extending through the geodetically topmost region of saidarrangement, at least one insulating coolant discharge line connected tosaid topmost portion, a coolant collector tank with a gas cushion spacemounted geodetically above said topmost ring conductor portion, saidcoolant discharge line forming a riser communicating from below withsaid tank so that said riser conducts into said tank not only coolantbut, due to buoyancy, also entrained undissolved gas, the coolingbranches of the circuit connectors between each two of saidfeed-throughs having approximately in the middle of their cooling-ductlength a topmost ring conductor portion, at least one coolant dischargeline connected to said topmost portion so that at least one pair ofcoolant stream paths is formed, one path of each pair passing directlyvia a circuit connector cooling duct to a connection point of saidcoolant discharge line, and one of each of said path pairs extending tosaid connection point through insulating hose members that fluidicallyinterconnect connectors of different phases or different potentials.

3. A liquid-cooled electric machine, such as a turbogenerator, with astator having a multiphase doublelayer lap winding composed of windingportions, main current feed-throughs, and circuit connectors which formelectric circuit group connections between said winding portions andwhich connect said winding portions with said feed-throughs, said statorcomprising a liquid-coolant system having two hydraulically parallelconnected branch groups of coolant ducts of which a first one extendsthrough said multi-phase winding, the second branch group extendingthrough said feedthroughs and said connectors, insulating hose membersforming part of said second branch group and fluidically bridging eachtwo of said connectors that have different instantaneous electricalpotentials respectively, a plurality of hydraulically parallel coolingbranches of said second group being formed by said hose members of thoseof said connectors that are electrically located between each two ofsaid feedthroughs, said connectors forming a ring conductor arrangement,each of said cooling branches between two respective ones of saidfeed-throughs having a portion extending through the geodeticallytopmost region of said arrangement, at least one insulating coolantdischarge line connected to said topmost portion, a coolant collectortank with a gas cushion space mounted geodetically above said topmostring conductor portion, said coolant discharge line forming a risercommunicating from below with said tank so that said riser conducts intosaid tank not only coolant but, due to buoyancy, also entrainedundissolved gas, each of said two cooling branch groups comprising asupply distribution line, a discharge manifold and insulating ductmembers with metal fittings which connect said supply distribution lineand said manifold with cooling branch parts at ground potential so as topermit, with the cooling branches filled with water, an insulation testof one stator winding when other winding circuits or cooling branchparts not supposed to conduct testing current are held at the measuringpotential different from ground potential.

4. In a machine according to claim 3, said insulating duct membersforming resilient compensators.

5. In a machine according to claim 3, said insulating duct members beingformed of corrugated bellons tubing.

1. A liquid-cooled electric machine having a three-phase stator windingin simple Y connection, such as a turbo-generator, with a stator havinga multi-phase double-layer lap winding composed of winding portions,main current feed-throughs, six of said feedthroughs being associated inpairs with each one of said stator winding circuits, and circuitconnectors which form electric circuit group connections between saidwinding portions and which connect said winding portions with saidfeed-throughs, said stator comprising a liquid-coolant system having twohydraulically parallel connected branch groups of coolant ducts of whicha first one extends through said multi-phase winding, the second branchgroup extending through said feed-throughs and said connectors,insulating hose members forming part of said second branch group andfluidically bridging each two of said connectors that have differentinstantaneous electrical potentials respectively, a plurality ofhydraulically parallel cooling branches of said second group beingformed by said hose members of those of said connectors that areelectrically located between each two of said feed-throughs, saidconnectors forming a ring conductor arrangement, each of said coolingbranches between two respective ones of said feed-throughs having aportion extending through the geodetically topmost region of saidarrangement, at least one insulating coolant discharge line connected tosaid topmost portion, a coolant collector tank with a gas cushion spacemounted geodetically above said topmost ring conductor portion, saidcoolant discharge line forming a riser communicating from below withsaid tank so that said riser conducts into said tank not only coolantbut, due to buoyancy, also entrained undissolved gas, said circuitconnectors comprising external terminal connectors which establish theelectrical connection between said feedthroughs and an end of thewinding circuit, and internal circuit-group connectors whichelectrically series connect respective parts of said windings, saidsecond cooling branch group forming six hydraulically parallel flowpaths through the cooling ducts of the connectors, each individual oneof said six paths extending through the series-connected cooling ductsof a feed-through, a circuit connector, an insulating hose sectionfluidically bridging the phase jump to the group circuit connector ofanother circuit of the winding, and thence through part of said topmostportion of said ring conductor to the cooling discharge line.
 2. Aliquid-cooled electric machine having a three-phase stator winding indouble-Y connection, such as a turbo-generator, with a stator having amulti-phase double-layer lap winding composed of winding portions, mAincurrent feed-throughs, six of said feed-throughs being pairwiseassociated with each of the stator winding phases, and circuitconnectors which form electric circuit group connections between saidwinding portions and which connect said winding portions with saidfeed-throughs, said stator comprising a liquid-coolant system having twohydraulically parallel connected branch groups of coolant ducts of whicha first one extends through said multi-phase winding, the second branchgroup extending through said feed-throughs and said connectors,insulating hose members forming part of said second branch group andfluidically bridging each two of said connectors that have differentinstantaneous electrical potentials respectively, a plurality ofhydraulically parallel cooling branches of said second group beingformed by said hose members of those of said connectors that areelectrically located between each two of said feed-throughs, saidconnectors forming a ring conductor arrangement, each of said coolingbranches between two respective ones of said feed-throughs having aportion extending through the geodetically topmost region of saidarrangement, at least one insulating coolant discharge line connected tosaid topmost portion, a coolant collector tank with a gas cushion spacemounted geodetically above said topmost ring conductor portion, saidcoolant discharge line forming a riser communicating from below withsaid tank so that said riser conducts into said tank not only coolantbut, due to buoyancy, also entrained undissolved gas, the coolingbranches of the circuit connectors between each two of saidfeed-throughs having approximately in the middle of their cooling-ductlength a topmost ring conductor portion, at least one coolant dischargeline connected to said topmost portion so that at least one pair ofcoolant stream paths is formed, one path of each pair passing directlyvia a circuit connector cooling duct to a connection point of saidcoolant discharge line, and one of each of said path pairs extending tosaid connection point through insulating hose members that fluidicallyinterconnect connectors of different phases or different potentials. 3.A liquid-cooled electric machine, such as a turbo-generator, with astator having a multi-phase double-layer lap winding composed of windingportions, main current feed-throughs, and circuit connectors which formelectric circuit group connections between said winding portions andwhich connect said winding portions with said feed-throughs, said statorcomprising a liquid-coolant system having two hydraulically parallelconnected branch groups of coolant ducts of which a first one extendsthrough said multi-phase winding, the second branch group extendingthrough said feed-throughs and said connectors, insulating hose membersforming part of said second branch group and fluidically bridging eachtwo of said connectors that have different instantaneous electricalpotentials respectively, a plurality of hydraulically parallel coolingbranches of said second group being formed by said hose members of thoseof said connectors that are electrically located between each two ofsaid feed-throughs, said connectors forming a ring conductorarrangement, each of said cooling branches between two respective onesof said feed-throughs having a portion extending through thegeodetically topmost region of said arrangement, at least one insulatingcoolant discharge line connected to said topmost portion, a coolantcollector tank with a gas cushion space mounted geodetically above saidtopmost ring conductor portion, said coolant discharge line forming ariser communicating from below with said tank so that said riserconducts into said tank not only coolant but, due to buoyancy, alsoentrained undissolved gas, each of said two cooling branch groupscomprising a supply distribution line, a discharge manifold andinsulating duct members with metal fittings which connect said supplydistribution line and said manifold with cooling branCh parts at groundpotential so as to permit, with the cooling branches filled with water,an insulation test of one stator winding when other winding circuits orcooling branch parts not supposed to conduct testing current are held atthe measuring potential different from ground potential.
 4. In a machineaccording to claim 3, said insulating duct members forming resilientcompensators.
 5. In a machine according to claim 3, said insulating ductmembers being formed of corrugated bellons tubing.